The present disclosure generally relates to superconductors, and more particularly relates to a multi-qubit tunable coupling architecture using superconducting qubits.
Quantum computation is based on the reliable control of quantum bits. The fundamental operations required to realize quantum algorithms are a set of single-qubit operations and one two-qubit operations which establish correlations between two separate quantum bits. The realization of high fidelity two-qubit operations is required both for reaching the error threshold for quantum computation and for reaching reliable quantum simulations.
Currently for superconducting qubits the single-qubit gates and are implemented with microwave controls. There are three main types of two qubit gates: 1) gates based on tunable frequency qubits, 2) gates based on microwave-driven qubits (e.g., cross-resonance, flick fork, Bell Rabi, MAP, sideband transitions, and 3) gates based on geometric phases (e.g., resonator-induced phase gate, holonomic gates).
For gates based on tunable frequency qubits, the qubits themselves are tuned in frequency to activate a resonant interaction. These gates essentially have two operating points: an ‘off’-position with essentially zero coupling and an ‘on’ position when the qubits have a strong two-qubit interaction. These gates have a very good on-off ratio, but because the qubits are tunable via externally applied magnetic flux, they can be limited by 1/f noise which limits the coherence of the qubits to a few microseconds.
For gates based on microwave-driven qubits, the qubits can be designed to be fixed in frequency so they are immune to flux noise. However, to activate the gate requires microwave pulses. The problems with these gates are that they have a low on/off ratio and are very hard to address the gate of interest without activating unwanted interactions.
Gates based on geometric phases are based on the path of the quantum state in its state space and the acquired quantum phase associated with this excursion. Adiabatic geometric gates are robust against certain types of noise, but are generally slow and require the controls to adiabatic. Non-adiabatic gates can be faster and potentially share the noise-resilience of their adiabatic cousins.